Point issue triage at GitHub; tidy overlay Svelte modules

[sm17p]

Summary

• Update Cursor issue-refinement workflow to treat GitHub issues as the source of truth (no local docs/ISSUE_REFINEMENTS.md).
• Adjust skill-maintenance, skill-hygiene, and pr-from-issue skills accordingly.
• Reformat and tidy overlay-related Svelte (measurements, ruler, side panel, SVG manager, extension settings, shared components).

Test plan

• pnpm check
• pnpm lint
• Smoke: open extension on a page, toolbar, side panel, measurements/ruler as touched

Made with Cursor

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